High frequency electric transformers



Sept. 2, 1958 w. F. GLOVER 2,850,709

HIGH FREQUENCY ELECTRIC TRANSFORMERS Filed April 28. 1954 2 I 2 /0 '5 a 2 x Inventor W; F. GLOVER yfwfizfifi Attorney nited States Patent HIGH FREQUENCY ELECTRIC TRANSFORMERS William Frank Glover, London, England, assignor to international Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application April 28, E54, Serial No. 426,109 2 Claims. (Cl. 336-232) This invention relates to electric transformers for use at high frequencies in the megacycle range, such as are commonly used in the intermediate frequency stages of microwave systems.

Such transformers may be required to deal with a he quency range extending, for example, from 50 to 90 rnc./s. The windings of these transformers must have very low self inductance values in the order of microhcnries or fractions of a microhenry and therefore will only consist of at the most a few turns and in order to get the desired values the windings have to be adjusted so that they consist of one or more complete turns and part of a turn.

It is one object of the present invention to provide a construction which will enable the windings of such transformers to be accurately adjusted to'fractions of a turn.

It is another object of the present invention to provide a construction which will enable the mutual inductance between primary and secondary windings to be accurately adjusted and then fixed in the adjusted condition.

It is a further object of the present invention to provide a construction in which the electrostatic coupling between the primary and secondary windings shall be as small as possible.

It is important for manufacturing economy that the transformers should be accurately reproducible.

In order to attain these objects a high frequency electric transformer is constructed which comprises two insulating plates each having at least one fiat surface, two flat spiral conducting windings each mounted on a fiat surface of a corresponding one of said insulating plates, a tubular casing of an insulating material within which the two bodies are mounted with the conducting spirals facing one another, and conducting leads connected to the ends of said spiral windings.

in constructing either a primary or a secondary winding for a transformer according to the present invention a number of turns of insulated wire are wound to form a spiral and the spiral is then coated with an adhesive material and caused to adhere to a flat surface of one of the said insulating plates. The adhesive material used is such that the insulated wire adheres to the insulating plate but not so firmly that it cannot be pulled away during the adjustment as will be explained. A suitable adhesive for this purpose is made up of polyvinyl formal dissolved in ethylene dichloride. When the solvent is driven off the spiral winding will be found to be adhering to the insulating plate but not so firmly that it cannot be unwound. Cellulose nitrate or cellulose acetate cements could equally be used. For the polyvinyl formal cement mentioned above it has been found that a mixture in the proportions of 3 gm. of polyvinyl formal in 28 milli-litres of ethylene dichloride is satisfactory.

The outer end of the spiral forming a winding is led along a notch in the peripheral edge of the insulating support plate to the flat surface of which the spiral is affixed and is attached to a terminal pin mounted in and projecting from the other side of the plate. The inner end of the spiral is led through an aperture in the centre of the insulating support plate and after adjustment as described below is attached to a second terminal pin also mounted on the other side of the support plate. I

The number of turns forming the spiral windings originally attached to the flat surfaces of the supporting bodies is in excess of the number finally required and the self inductance of each winding is finally adjusted by drawin g some of the wire forming the inner turns through the central aperture in the support plate before attaching it to the corresponding terminal, thus decreasing the total length of the wire forming the spiral and reducing the self inductance.

After the adjustment is completed an additional coating of quick setting adhesive may be applied.

T 0 construct a transformer two such plates, each carrying an adjusted spiral winding, are mounted facing one another inside a casing, which may conveniently be of circular cross-section.

The primary and secondary windings are wound in opposite directions to ensure that when their outer ends are at the same potential adjacent turns of the two windings will be at the same potential and the electrostatic coupling will be reduced to a minimum.

The mutual inductance is determined by the axial distance between the two windings and this can be adjusted by mounting the assembly in a jig provided with a threaded member to which one of the insulating plates is attached by its terminals. This threaded member can be provided with a micrometer adjustment and can be screwed in or out while the transformer is kept under test in a circuit which in effect measures the mutual inductance.

When the correct positions for the plates have been determined a suitable adhesive cement is fed into the open ends of the insulating tube and caused to set firmly after which the transformer can be removed from the jig. The space between the windings inside the tubular casing may befilled with a suitable hard setting compound if desired but this is not essential. A suitable cement for filling the open ends of the insulating tube and retaining the windings in position is made up of an ethoxylene resin in which there is dispersed a finely divided mineral material. A dispersion of 7.75 gm. of titanium dioxide in 5.0 gm. of ethoxylene resin, with the addition of a small quantity of a hardening material has been found suitable.

One embodiment of the invention will now be described with reference to the accompanying drawings in which:

Fig. 1 represents an external view of a transformer according to the invention,

Fig. 2 represents an end view of the transformer of Fig. 1,

Fig. 3 represents a cross-section in the plane AA indicated in Fig. 2,

Figs. 4, 5, 6, 7, 8 and 9 represent views of the windings on the support plates which are assembled to form the transformer.

In Fig. 1 there is shown the external view of a transformer according to the invention. The casing 1, which may conveniently be made of a synthetic resin or of a ceramic material, is preferably of circular cross-section. The terminals 2 from the two windings, primary and secondary, project from opposite ends of the tubular casing 1 through sealing cement plugs 10 which will be seen in Fig. 3.

In Fig. 2 there is shown an end view of the transformer with leads 2 as in Fig. 1. A section along plane AA of Fig. 2 yields Fig. 3.

In this figure the outer casing 1 is shown with the support plates 3 and 4 carrying the spiral windings 5 (primary) and 6 (secondary). The support plates 3 and 4 are mounted in the end portions of the casing l and the faces carrying the spiral windings are shown as separated from one another by a filling 7 which may consist of a solid dielectric such as for example a synthetic resin.

It is however not essential that any filling material 7 should be included between the plates.

The arrangement of the spiral windings can be clearly seen in Figs. 6 and 7. As explained earlier these windings are in opposite directions to reduce electrostatic coupling between them. Fig. 6 shows a winding with 1 /2 turns while Fig. 7 shows one with 2 /2 turns. Supports 3 and 4 are identical in shape and it can clearly be seen in Figures 4, 5, 8 and 9 how the inner turn of each winding is led through the centre hole 8 of the support while the outer turn is led through a notch 9 in the periphery of the support. After the outer end of the winding has been attached to its terminal 2 as shown in Figs. and 8 the inner end is drawn through the centre hole 3 until the desired self inductance is obtained, as indicated by measurements on a suitable device, after which it is attached to its corresponding terminal. This arrangement allows for very fine adjustment of the self inductance.

Turning again to Fig. 3 it can be seen that the support plates 3 and 4 are mounted in the ends of the tubular casing 1 and are held in position by adhesive cement plugs 10 which may conveniently be made of an ethoxylene resin loaded with a mineral powder such as titanium dioxide. The terminals 2 which are firmly mounted in the support plates 3 and 4 project through cement plugs 10.

By the construction described above very small transformers can be made with great accuracy. As an example transformers can be made of which the casing is 0.375 inch long and 0.312 inch in diameter.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What I claim is:

1. High frequency transformer comprising a tubular casing of insulating material, two insulating bodies fixed in said casing each body having a surface facing the corresponding surface of the other body, two spiral windings adherently mounted one on each of said corresponding surfaces, said windings being wound in opposite directions and adjusted so that when their outer ends are at the same potential adjacent turns of the two windings will also be at the same potential whereby electrostatic coupling is reduced to a minimum.

2. High frequency transformer as claimed in claim 1 in which each of said insulating bodies is provided with a notch in its periphery and a central aperture, the other end of each spiral winding extends along the peripheral notch in the body on which said winding is mounted, the inner end of each spiral winding extends through the central aperture of the said body and said ends are attached to terminals mounted on the outer surfaces of the respective bodies.

References Cited in the file of this patent UNITED STATES PATENTS 1,829,109 Pohu Oct. 27, 1931 1,837,678 Ryder Dec. 22, 1931 2,177,260 Laube Oct. 24, 1939 2,266,925 Verrill Dec. 23, 1941 2,404,185 Mann July .16, 1946 2,432,715 Benner et al Dec. 16, 1947 2,434,511 Osterman et al. Jan. 13, 1948 2,475,829 Fennema July 12, 1949 2,482,902 Clark Sept. 27, 1949 2,488,325 Peek Nov. 15, 1949 2,532,231 Jarvis Nov. 28, 1950 2,614,149 Steyer et al Oct. 14, 1952 FOREIGN PATENTS 53,143 France Nov. 13, 1944 OTHER REFERENCES Publication: RCA Developmental Printed-Circuit I. F. Transformers, Coils and Traps, March 1952. 

